This disclosure relates generally to powder-bed additive manufacturing apparatus and methods. More particularly, this disclosure relates to powder-bed additive manufacturing apparatus and methods for forming a substantially crack-free component. Significant advances in high temperature materials have been achieved through the formulation of Co-based, Ni-based, Ti-based and Fe-based alloys, known conventionally as “superalloys.” These alloys are typically primarily designed to meet mechanical property requirements, such as creep resistance and fatigue strengths. As such, modern metal alloys have found wide use in high temperature applications, such as use in gas turbine engines.
Metal alloys components, such as components of gas turbine engines, are typically cast and/or machined. Typically, a disposable core die (DCD) process is utilized to cast metal alloy components. A DCD casting method commonly entails using additive or other manufacturing methods to create a disposable shell that is utilized to form a ceramic core, and then subsequently using the ceramic core to conventionally cast the components. High pressure turbine blades are typically manufacturing utilizing such a method. However, current metal alloy component casting techniques, such as DCD, require expensive tooling and include high fabrication costs. Further, current metal alloy component casting techniques are limited in component design complexity and geometries due to draft angle limitations, the necessity to avoid overhangs, and other limitations that are inherent in the casting process.
Recently, additive manufacturing methods for making metal alloy components have emerged as alternatives to casting and machining methods. Additive manufacturing is also referred to as “layered manufacturing,” “laser sintering,” “reverse machining,” and “3-D printing.” Such terms are treated as synonyms for purposes of the present disclosure. On a basic level, additive manufacturing technologies are based on the concept of building up material in a cross-sectional layer-by-layer manner to form a 3D component. Common to additive manufacturing technologies is the use of a 3D modeling software (Computer Aided Design or CAD), machine equipment and layering material. Once a CAD sketch is produced, the machine equipment reads in data from the CAD file and uses successive layers of a desired material to fabricate the 3D component.
Unlike casting processes, additive manufacturing is not limited by the necessity to provide draft angles, avoid overhangs, etc. Additive manufacturing also simplifies and reduces the costs associated with metal alloy component manufacturing as compared to typical casting and machining methods. For example, additive manufacturing of turbine blades and other high temperature turbine components eliminates the expensive tooling needed for casting and machining, which results in significant cost and cycle time reductions.
Some specific additive manufacturing processes employ a powder bed fusion technique to fuse metal alloy powder in additive steps to produce a component. For example, some additive manufacturing processes utilize a beam of energy to fuse a layer of metal alloy powder in a powder bed in additive steps. Some examples of such powder bed additive manufacturing processes include direct metal laser sintering/fusion (DMLS)/(DMLF), selective laser sintering/fusion (SLS)/(SLF), and electron beam melting (EBM). In these processes, a layer of metal alloy powder in the powder bed is fused to an underlying partially-formed component (or a seed component) to add a new layer to the component. A new layer of metal alloy powder is deposited into the powder bed and over the previously formed layer of the partially-formed component, and the new layer of metal alloy powder is similarly fused to the component. The depositing-and-fusing procedure is repeated a number of times to produce a plurality of layers on the partially-formed component to, ultimately, form the metal alloy component.
Unfortunately, metal alloy components formed by powder bed fusion additive manufacturing techniques may experience cracking during formation (i.e., during the depositing-and-fusing procedure) and during post build processes or use. For example, some powder bed fusion additive manufacturing techniques may not maintain acceptable thermal profiles in the added layers that form the component during the build process, such as the cooling rate of a newly fused layer of metal alloy powder or a thermal gradient between a newly fused layer of metal alloy powder and an adjacent portion of the component. Unacceptable thermal profiles of the layers of a component formed by additive manufacturing tend to induce thermal stresses that have a tendency to produce cracks in the component.
Accordingly, it is desirable to provide improved additive manufacturing techniques, such as powder bed fusion additive manufacturing apparatus and methods, which reduce the tendency of the formed metal alloy component to crack—both during the build process and/or post-build. Further, it is desirable to provide metal alloy components for use in high temperature gas turbine engines quickly and efficiently. Other desirable features and characteristics of the disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.